Durability of Commercially Available GFRP Reinforcement in Seawater-Mixed Concrete under Accelerated Aging Conditions

The effect of seawater used as mixing water in concrete on the long-term properties of glass fiber–reinforced polymer (GFRP) bars is the focus of this work. The durability of GFRP bars embedded in seawater-mixed concrete was studied in terms of residual mechanical properties (i.e., tensile strength, horizontal and transverse shear strength, and GFRP–concrete bond strength) after immersion in seawater at 60°C for a period of 24 months. Benchmark specimens were also cast using conventional concrete. Results showed comparable performance in tensile and shear properties between the two sets of bars with some degradation of the mechanical properties in both cases. However, bond strength showed some differences between the two sets of bars. SEM was used to identify degradation mechanisms. Areas with large concentrations of voids near the bar edge, formed during manufacturing, may provide a pathway for moisture and alkalis, which could lead to the fiber disintegration and debonding between fibers and the resin. Over time, a greater number of fibers are affected, which leads to the formation of significant cracking near the edge. Results were qualitatively similar for embedded bars in seawater-mixed and conventional concrete, explaining a similar reduction in tensile properties, horizontal shear strength, and transverse shear strength seen in both sets of bars. However, the bond strength does not significantly decrease in these specimens over time for unclear reasons.